The over-all objective of this proposal is to elucidate the role of the decidual tissue in the regulation of corpus luteum function in pregnant and pseudopregnant rats. The first approach, using transplantation and radioimmunoassay, will be determine whether the decidual tissue (DT) of pregnant rats, like the DT of pseudopregnant animals, sustain progesterone synthesis in the absence of prolactin. Using hypophysectomized animals we will determine whether the luteotropic effect of the decidual tissue is related to the presence of LH or estrogen. The possibility that the decidual tissue stimulates, like prolactin, the generation of both LH and estradiol receptor will then be investigated using a radioreceptor technique. Finally, we will determine whether the DT-hormone bind, as does rat placental lactogen to the same receptor site than prolactin, and if so the levels of the DT-hormone will be measured in the DT and in the serum.